Arrowleafed Monochoria (Monochoria vaginalis) is a monocot plant in the pontederiaceae family. A single amino acid substitution from Aspartate 376 to Glutamate has led to resistance to ALS inhibitors as indicated in the table below.

Monochoria vaginalis is one of the most serious weeds of rice fields in Asia. The species is predominantly selfing. To reveal the potential for multiple mutational events, outcrossing and gene flow in the sulfonylurea-resistant (SU-R) M. vaginalis populations, we investigated (i) if each SU-R population was a single SU-R biotype or a mixture of several SU-R biotypes using restriction analysis or direct sequencing of acetolacatate synthase (ALS) genes and (ii) genetic diversity of SU-R and -susceptible (S) populations using amplified fragment length polymorphism (AFLP) analysis. Nineteen or 20 individuals were sampled from four SU-R and five SU-S populations respectively. Amino acid substitutions conferring resistance in the SU-R populations were Pro197Ser in the ALS1 or ALS3, or Asp376Glu in the ALS1 and each SU-R population was composed of a single SU-R biotype. In cluster analysis each SU-R individual formed a cluster, whereas the individuals from a SU-S population belonged to different clusters. Some SU-R populations showed polymorphic AFLP loci. The results indicated that these SU-R biotypes emerged from a single mutational event and any gene flow of SU-R genes from adjacent populations did not occur. A low level of outcrossing and recombinations of SU-R genes occurred within some SU-R populations of M. vaginalis..